Accumulation of GCT cells in either in the G1/G0 or G2/M phase of the cell cycle and the induction of apoptosis pointed at an alternative mode of action of PaRi apart from the canonical CDK4–RB1 axis, prompting us to decipher the molecular mode of action of PaRi in GCT cells in more detail. This evidence concerns the gene RB1 and granular cell tumor.